1. Field of the Invention
This invention relates to an .alpha.-cyanoacrylate adhesive composition of matter excellent in storage stability and high in viscosity and having a thixotropy.
2. Prior Art
.alpha.-cyanoacrylate is a compound expressed by the general formula: ##STR1## wherein R represents alkyl, allylalkyl, aralkyl, haloalkyl, cyclohexyl, phenyl groups and has a property susceptible to anionic polymerization and liable to be polymerized and set within a very short time of several seconds to several minutes at a normal temperature without using a catalyst by the anionic active factor in the moisture on the surface of a solid, humidity in the atmosphere, and alkaline substances. Because of the property described, the .alpha.-cyanoacrylate adhesive composition finds wide application both in industrial use and in home use for adhesion of rubber, metal, glass, plastic, wood, ceramic, etc.
Because almost all .alpha.-cyanoacrylate adhesives are low in viscosity, they have not only the disadvantage that when applied to a vertical surface, they hang from the surface, or when applied to a porous material, they are sucked in the material, but also the disadvantage that they are not stringing (roping) from the adhesive applied surface. In other words, there was formerly no such composition of matter as .alpha.-cyanoacrylate superior in workability and having substantial thixotropy.
Generally, the fact that a substance has a thixotropy means that the substance becomes low in viscosity under high shearing and becomes high in viscosity under low shearing but the thixotropy constitutes an important factor in determining workability when a liquid material such as an adhesive and paint is handled. Therefore, it has long been desired to develop an .alpha.-cyanoacrylate adhesive superior in storage stability and high in viscosity and having a thixotropy.
In view of the circumstances above, it was recently proposed in U.S. Pat. No. 4,477,607 that hydrophobic fumed silica (of ultramicro particle powder) having a surface treated with a trialkoxyalkylsilane be added to .alpha.-cyanoacrylate, but as shown in the examples to be later described, the stability of the proposed invention at a temperature of 70.degree. C. keeps effective for five days and has not yet been sufficiently improved in thixotropy.